Adams, Katherine H., author
Mayfield Publishing Company, 2000
Buku Teks
Young, Felina C., author
IPWI, 1999
Buku Teks
Roemer, John E
Institute of International Studies, University of California, 1975
Buku Teks
Distributed by Almqvist & Wiksell International, 1974
Buku Teks
Dietsch, Betty Mattix, author
McGraw-Hill, 2003
Buku Teks